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Bacteria use the same genes to fight fungi and humans


Many of the genes bacteria use to infect fungi are the same ones they use to cause disease in humans, a new study reports. Some of these genes produce secreted proteins and hair-like surface appendages. By understanding the ancient battle between bacteria and fungi, researchers may gain insights into how pathogens infect humans.

Left: Fungal filament after incubation with the bacterium for one minute. Right: Bacterial attachments to the filament after 48 hours.

"We tend to think bacteria only want to kill humans, but they've actually been selected to behave this way for billions of years," says Roberto Kolter, who led the study with his colleague Deborah A. Hogan at Harvard Medical School in Boston, Massachusetts.

The researchers investigated the interaction between two human pathogens: the fungus Candida albicans and the bacterium Pseudomonas aeruginosa. Under certain conditions, the bacterium kills the fungus. In humans, it can infect the lungs of patients with cystic fibrosis.

The researchers knew some of the genes bacteria use to cause human infection, so they tested whether the same genes were used against fungi. They found that bacteria employed many of the same infectious agents against the fungus as in humans, including quorum sensing mechanisms, secreted toxins and pili (surface attachments).

The team also discovered that the fungus appears to have a defense mechanism against bacterial assault: It assumes a yeast-like form that blocks the growth of deadly communities of bacteria, or biofilms. (This finding was not reported in the Science paper.)

The antagonism between pathogenic fungi and bacteria has likely led to the evolution and maintenance of infectious genes, the authors conclude in Science.

"As researchers, we need a broader view of virulence," says Kolter. "Most of the research has focused on how bacteria interact with bigger organisms, but they have interacted with smaller organisms like fungi for longer and in a wider ecological world."

See related GNN story
»Fighting bacteria with inside information

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Hogan, D. et al. Pseudomonas-Candida Interactions: An ecological role for virulence factors. Science 496, 2229-2231 (June 21, 2002).

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